Fluoxetine

| Section2 = | Section3 = | Section4 = }} Fluoxetine (also known by the tradenames Prozac, Sarafem) is an antidepressant of the selective serotonin reuptake inhibitor (SSRI) class. It is manufactured and marketed by Eli Lilly and Company. In combination with olanzapine it is known as symbyax.

Fluoxetine is approved for the treatment of major depression (including pediatric depression), obsessive-compulsive disorder (in both adult and pediatric populations), bulimia nervosa, panic disorder and premenstrual dysphoric disorder.

Despite the availability of newer agents, fluoxetine remains extremely popular. Over 22.2 million prescriptions for generic formulations of fluoxetine were filled in the United States in 2007, making it the third most prescribed antidepressant after sertraline (SSRI that became generic in 2006) and escitalopram (non-generic SSRI).

Mechanism of action

Fluoxetine's mechanism of action is primarily that of an SSRI although it may produce some of its effects through 5-HT_2C antagonism in a manner similar to the novel antidepressant agomelatine. Other psychopharmacological substances that exhibit 5-HT_2C antagonism are mirtazapine, trazodone, some tricyclic antidepressants and various (mainly atypical) antipsychotics.

History

The work which eventually led to the discovery of fluoxetine began at Eli Lilly and Company in 1970 as a collaboration between Bryan Molloy and Robert Rathbun. It was known at that time that the antihistamine diphenhydramine shows some antidepressant-like properties. 3-Phenoxy-3-phenylpropylamine, a compound structurally similar to diphenhydramine, was taken as a starting point, and Molloy synthesized dozens of its derivatives. Testing the physiological effects of these compounds in mice resulted in nisoxetine, a selective norepinephrine reuptake inhibitor currently widely used in biochemical experiments.

Later, hoping to find a derivative inhibiting only serotonin reuptake, another Eli Lilly scientist, David Wong, proposed to retest the series for the in vitro reuptake of serotonin, norepinephrine and dopamine. This test, carried out by Jong-Sir Horng in May 1972, Wong would publish the first article about fluoxetine in 1974. A year later, it was given the official chemical name fluoxetine and the Eli Lilly and Company gave it the trade name Prozac. In February 1977, Dista Products Company, a division of Eli Lilly & Company, presented a new drug request to the U.S. Food and Drug Administration (FDA) for fluoxetine.

A controversy ensued after Lilly researchers published a paper titled "Prozac (fluoxetine, Lilly 110140), the first selective serotonin uptake inhibitor and an antidepressant drug" Fluoxetine made its appearance on the Belgian market in 1986 and was approved for use by the FDA in December 1987. Fluoxetine was the fourth SSRI to make it to market, after zimelidine, indalpine and fluvoxamine. However, the first two were withdrawn due to the side effects, and a vigorous marketing campaign by Eli Lilly made sure that in the popular culture fluoxetine has been perceived as a scientific breakthrough and associated with the title of the first SSRI.

Eli Lilly's patent on Prozac (fluoxetine) expired in the United States in August 2001, prompting an influx of generic drugs onto the market. Prozac was rebranded "Sarafem" for the treatment of PMDD in an attempt to stem the post-patent decrease in Eli Lilly's sales of fluoxetine.

Indications

Fluoxetine has been approved by the FDA for the treatment of major depression, obsessive compulsive disorder, bulimia nervosa and panic disorder. Fluoxetine was shown to be effective for depression in 6-week long double-blind controlled trials, where it also alleviated anxiety and improved sleep. Fluoxetine was better than placebo for the prevention of depression recurrence when the patients, who originally responded to fluoxetine, were treated for a further 38 weeks. Efficacy of fluoxetine for geriatric, as well as pediatric, depression was also demonstrated in placebo-controlled trials. Furthermore, 5 mg/day fluoxetine was shown to be better than placebo and similar to 20 mg/day, and one weekly dose of 80 mg fluoxetine was equivalent to 60 mg/day fluoxetine or 150 mg/day amitriptyline.

OCD was successfully treated by fluoxetine in two adult and one pediatric placebo-controlled 13-week trials. The higher doses of fluoxetine appeared to result in better response, while the reverse relationship was observed in the treatment of depression. Similarly to other SSRIs, sexual side effects are common with fluoxetine; they include anorgasmia and reduced libido.

In addition, rash or urticaria, sometimes serious, was observed in 7% patients in clinical trials; one-third of these cases resulted in discontinuation of the treatment. Postmarketing reports note several cases of complications developed in patients with rash. The symptoms included vasculitis and lupus-like syndrome. Death has been reported to occur in association with these systemic events. Akathisia usually begins after the initiation of the treatment or increase of the dose and disappears after fluoxetine is stopped or its dose is decreased, or after treatment with propranolol. There are case reports directly linking akathisia with suicidal attempts, with patients feeling better after the withdrawal of fluoxetine, and again developing severe akathisia on repeated exposure to fluoxetine. These patients described "that the development of the akathisia made them feel suicidal and that it had precipitated their prior suicide attempts." More rarely, fluoxetine has been associated with related movement disorders acute dystonia and tardive dyskinesia.

Fluoxetine taken during pregnancy also increases rate of poor neonatal adaptation. A study of fluoxetine administered to newborn mice found that early postnatal exposure of the drug later caused the adult mice to exhibit depressive and anxious behavior similar to those of induced depression, which could be relieved by fluoxetine. The American Association of Pediatrics classifies fluoxetine as a drug for which the effect on the nursing infant is unknown but may be of concern.

Discontinuation syndrome

Several case reports in the literature describe severe withdrawal or discontinuation symptoms following an abrupt interruption of fluoxetine treatment, popularly referred to as "Prozac Poopout". However, various studies have shown that the side effects of the fluoxetine discontinuation are rare and mild, especially compared to paroxetine, venlafaxine and fluvoxamine. The double-blind controlled studies support this opinion. No increase in side effects was observed in several studies when the treatment with fluoxetine was blindly interrupted for a short time (4–8 days) and then reinstated, this result being consistent with its slow elimination from the body. More side effects occurred during the interruption of sertraline (Zoloft) in these studies, and significantly more during the interruption of paroxetine. In a longer, 6 week-long, blind discontinuation study, an insignificantly higher (32% vs 27%) overall rate of new or worsened side effects was observed in the group that discontinued fluoxetine than in the group that continued treatment. However, a significantly higher 4.2% rate of somnolence at week 2 and 5-7% rate of dizziness at weeks 4-6 were reported by the patients in the discontinuation group. This prolonged course of the discontinuation symptoms, with dizziness persisting to the end of the study, is also consistent with the long half-life of fluoxetine in the body. According to a 2007 summary report of available evidence, fluoxetine has the lowest incidence of discontinuation syndrome among several antidepressants including paroxetine and venlafaxine. See also SSRI discontinuation syndrome.

Suicidality

The suicidality of fluoxetine can be determined on various levels of specificity. It can be determined on the antidepressant level, on the SSRI level, and on the fluoxetine level—fluoxetine is an SSRI antidepressant. The more specific level, the fewer studies can be used in a meta-analysis of clinical trials on that level.

Antidepressant

On the antidepressant level, the FDA requires all antidepressants to carry a black box warning stating that antidepressants may increase the risk of suicide in persons younger than 25. This warning is based on statistical analyses conducted by two independent groups of the FDA experts that found a 2-fold increase of the suicidal ideation and behavior in children and adolescents, and 1.5-fold increase of suicidality in the 18–24 age group. The suicidality was slightly decreased for those older than 24, and statistically significantly lower in the 65 and older group. This analysis was criticized by Donald Klein, who noted that suicidality, that is suicidal ideation and behavior, is not necessarily a good surrogate marker for completed suicide, and it is still possible that antidepressants may prevent actual suicide while increasing suicidality. This opinion goes against the general consensus that "suicidal ideation has been associated with suicide attempt in retrospective studies and with suicide in prospective studies."

SSRI

On the SSRI level, see the article SSRI, section Suicidality.

Fluoxetine

On the fluoxetine level, data is harder to come by than on the antidepressant and SSRI levels, as suicidal ideation and behavior in clinical trials are rare. For the above analysis on the antidepressant level, the FDA had to combine the results of 295 trials of 11 antidepressants for psychiatric indications to obtain statistically significant results. Considered separately, fluoxetine use in children increased the odds of suicidality by 50% (not statistically significant due to the low number of cases), and in adults decreased the odds of suicidality by approximately 30% (statistically significant).

Pharmacokinetics

isoenzyme CYP2D6. CYP2D6 is responsible for converting fluoxetine to its only active metabolite, norfluoxetine. Both drugs are also potent inhibitors of CYP2D6.]]

The bioavailability of fluoxetine is relatively high (72%), and peak plasma concentrations are reached in 6 to 8 hours. It is highly bound to plasma proteins, mostly albumin.

Fluoxetine is metabolized in the liver by isoenzymes of the cytochrome P450 system, including CYP2D6. The role of CYP2D6 in the metabolism of fluoxetine may be clinically important, as there is great genetic variability in the function of this enzyme among people. Only one metabolite of fluoxetine, norfluoxetine (N-demethylated fluoxetine), is biologically active.

The extremely slow elimination of fluoxetine and its active metabolite norfluoxetine from the body distinguishes it from other antidepressants. With time, fluoxetine and norfluoxetine inhibit their own metabolism, so fluoxetine elimination half-life changes from 1 to 3 days, after a single dose, to 4 to 6 days, after long-term use. Similarly, the half-life of norfluoxetine is longer (16 days) after long-term use. Therefore, the concentration of the drug and its active metabolite in the blood continues to grow through the first few weeks of treatment, and their steady concentration in the blood is achieved only after four weeks. Moreover, the brain concentration of fluoxetine and its metabolites keeps increasing through at least the first five weeks of treatment. That means that the full benefits of the current dose a patient receives are not realized for at least a month since its initiation. For example, in one 6-week study, the median time to achieving consistent response was 29 days.

Fluoxetine is a selective serotonin reuptake inhibitor and does not appreciably inhibit norepinephrine and dopamine reuptake. Nevertheless, Eli Lilly researchers found that a single injection of a rat with a large dose of fluoxetine also results in a significant increase of brain concentrations of norepinephrine and dopamine. This effect may be mediated by 5HT2a and, in particular, 5HT2c receptors, which are inhibited by higher concentrations of fluoxetine. The Ely Lilly scientists also suggested that the effects on dopamine and norepinephrine may contribute to the antidepressant action of fluoxetine. The dopamine and norepinephrine increase was not observed at a smaller, more clinically relevant dose of fluoxetine. Similarly, in electrophysiological studies only larger and not smaller doses of fluoxetine changed the activity of rat's norepinephrinergic neurons. Some authors, however, argue that these findings may still have clinical relevance for the treatment of severe illness with supratherapeutic doses (60–80 mg) of fluoxetine. Among SSRIs, 'fluoxetine is the least "selective" of all the SSRIs, with a 10-fold difference in binding affinity between its first and second neural targets (i.e., the serotonin and norepinephrine uptake pumps, respectively).' Anything greater than a 10-fold difference results in insignificant activation of the secondary neuronal targets.

Besides its well-known effects on serotonin, fluoxetine also increases density of endogenous opioid receptors in the brains of rats. It is unclear if this occurs in humans, but if so it might account for some of fluoxetine's antidepressant and/or side effect profile.

Measurement in body fluids

Fluoxetine and norfluoxetine may be quantitated in blood, plasma or serum to monitor therapy, confirm a diagnosis of poisoning in hospitalized patients or assist in a medicolegal death investigation. Blood or plasma fluoxetine concentrations are usually in a range of 50-500 μg/L in persons taking the drug for its antidepressant effects, 900-3000 μg/L in survivors of acute overdosage and 1000-7000 μg/L in victims of fatal overdosage. Norfluoxetine concentrations are approximately equal to those of the parent drug during chronic therapy, but may be substantially less following acute overdosage, since it requires at least 1–2 weeks for the metabolite to achieve equilibrium.

Interactions

Fluoxetine and norfluoxetine inhibit many isozymes of the cytochrome P450 system that make drug metabolism possible. Both are potent inhibitors of CYP2D6 (the main enzyme responsible for their metabolism) and mild to moderate inhibitors of CYP1A2, CYP2B6, CYP2C9/2C19, and CYP3A4; furthermore, they inhibit the activity of P-glycoprotein, a type of membrane transport protein that plays an important role in drug transport and metabolism. This extensive effect on the body's pathways for drug metabolism creates the potential for interactions with many commonly used drugs.

The simultaneous use of fluoxetine with triptans, tramadol or other serotonergic agents can result in a rare, but potentially life-threatening adverse drug reaction called serotonin syndrome.

Controversy

In 1989, Joseph Wesbecker shot and killed eight people and injured 12 others before killing himself at his place of work in Kentucky. Wesbecker had been taking the selective serotonin reuptake inhibitor (SSRI) antidepressant fluoxetine for four weeks before these homicides, and this led to a legal action against the makers of fluoxetine, Eli Lilly. The case was tried and settled in 1994, and as part of the settlement a number of pharmaceutical company documents about drug-induced activation were released into the public domain. Subsequent legal cases have further raised the possibility of a link between antidepressant use and violence.

The Prozac Survivors Support Group created a report on 288 individuals who had suffered adverse effects from Fluoxetine during 1991 and 1992. It showed that most of the cases led to violence against self or other individuals. There were 164 cases in the suicide and suicide ideation category, including 34 complete suicides. There were also 133 cases of crime and violence, which featured 14 murders, nine attempted murders, 39 violent actions, 54 violent preoccupations and 17 crimes. The report also showed that 13 individuals had become addicted to Fluoxetine and 14 cases of alcoholism forming or worsening.

A meta-analysis published in February 2008 combined 35 clinical trials of four newer antidepressants (fluoxetine, paroxetine (Paxil), nefazodone (Serzone) and venlafaxine (Effexor)). These antidepressants belonging to three different pharmacological groups were considered together, and the authors did not analyze them separately. The authors concluded that "although the difference [between the placebo and antidepressants] easily attained statistical significance", it did not meet the criterion for clinical significance, as used by National Institute for Health and Clinical Excellence (UK), "for any but the most severely depressed patients." Some articles in the press using the titles "The creation of the Prozac myth" and "Prozac does not work in majority of depressed patients" presented these general findings about the relative efficacy of antidepressants and placebo as the findings about ineffectiveness of fluoxetine. In a follow-up article, the authors of the meta-analysis noted that "unfortunately, during its initial coverage, the media often portrayed the results as “antidepressants do not work”, which misrepresented our more nuanced pattern of findings."

As of April 2, 2010, Fluoxetine (Prozac) is one of four antidepressant drugs that the FAA will allow pilots to take without automatically prohibiting them from piloting an aircraft. The others are Sertraline (Zoloft), Citalopram (Celexa), and Escitalopram (Lexapro).

In popular culture

Because of its wide appeal as a popular antidepressant, Prozac has had numerous references to it in popular culture, including many books, movies, and songs. For example, the book Listening to Prozac was written in 1993 by psychiatrist Peter D. Kramer. The memoir Prozac Nation was written in 1994 by Elizabeth Wurtzel; it was made into a movie of the same name in 2001, starring Christina Ricci. Jill Sobule and Elise Thoron wrote the musical Prozak and the Platypus, which opened Off-Broadway in 2005. Lily Allen also mentioned Prozac in her song 'Everyone's At it'.

References

External links

Psychiatric Drug Facts with Dr. Peter Breggin

Biography of Dr. David T. Wong, one of the inventors of Prozac

Biography of Dr. Bryan B. Molloy, one of the inventors of Prozac

Biography of Dr. Ray Fuller, one of the inventors of Prozac

Trouble in Prozac – Fortune Magazine

U.S. National Library of Medicine: Drug Information Portal – Fluoxetine

Category:Selective serotonin reuptake inhibitors Category:Eli Lilly and Company Category:World Health Organization essential medicines Category:Phenol ethers Category:Organofluorides